internal/Painter: remove configurable edge FBA, use fallback alloc

This removes the configurable FBA for the edge cache, moving it to a
fallback allocator instead, with the FBA being a much smaller size, so
that we respect the stack a lot more.

The FBA should be enough for 64 edges worst-case scenario each edge is 4
bytes and may be duplicated in the final edge set, so 64*4*2 =
512 bytes. Note that not all edges make it into the final edge set
(e.g., during non-zero fill), hence why we say worst-case. This can and
will be optimized eventually to allow for more.

src/Context.zig

@@ -8,23 +8,14 @@ const Context = @This();
 const mem = @import("std").mem;
 
 const options = @import("options.zig");
-const paintpkg = @import("internal/Painter.zig");
 
+const Painter = @import("internal/Painter.zig");
 const Path = @import("Path.zig");
 const Pattern = @import("pattern.zig").Pattern;
 const Surface = @import("surface.zig").Surface;
 const Transformation = @import("Transformation.zig");
 const PathError = @import("errors.zig").PathError;
 
-/// The default value to use for the edge cache during rasterization, in number
-/// of edges that can be stored per scanline.
-///
-/// Note that this cannot be modified in the context. If you require a
-/// different value, either due to OOM issues due to a large number of edges,
-/// or if you want a smaller buffer, see internal/Painter.zig. Note that this
-/// API is currently unstable.
-comptime default_edge_cache_size: usize = 1024,
-
 /// The underlying surface.
 surface: Surface,
 
@@ -100,7 +91,7 @@ transformation: Transformation = Transformation.identity,
 ///
 /// This is a no-op if there are no nodes.
 pub fn fill(self: *Context, alloc: mem.Allocator, path: Path) !void {
-    try (paintpkg.Painter(self.default_edge_cache_size){ .context = self }).fill(alloc, path.nodes);
+    try (Painter{ .context = self }).fill(alloc, path.nodes);
 }
 
 /// Strokes a line for the path(s) in the supplied set.
@@ -115,5 +106,5 @@ pub fn fill(self: *Context, alloc: mem.Allocator, path: Path) !void {
 ///
 /// This is a no-op if there are no nodes.
 pub fn stroke(self: *Context, alloc: mem.Allocator, path: Path) !void {
-    try (paintpkg.Painter(self.default_edge_cache_size){ .context = self }).stroke(alloc, path.nodes);
+    try (Painter{ .context = self }).stroke(alloc, path.nodes);
 }